Browsing by Author "Sharma, Akanshu"

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Open Access
3rd International Symposium on Connections between Steel and Concrete : Stuttgart, Germany, 27th - 29th September 2017 ; proceedings
(Stuttgart : Institute of Construction Materials, University of Stuttgart, 2017) Sharma, Akanshu; Hofmann, Jan
Steel is an integral part of any concrete construction either in the form of anchors connecting structural/non-structural components to the structure or in the form of reinforcement embedded in concrete or sometimes as a part of steel-concrete composite construction. To ensure structural integrity, it is essential to form a reliable connection between steel and concrete. The anchorage must serve its function well to ensure the interaction between the components connected to the structure and the structure itself. The bond between reinforcement and concrete must be ensured to maintain the required flow of forces from concrete to steel and vice-versa. The concrete and steel structural members must be able to interact with each other in a desired way. If the connection between steel and concrete loses its integrity, the integrity of the entire structure comes in jeopardy. In order to ensure the integrity of connections between steel and concrete, it is required to (i) investigate their behavior through high quality experiments, (ii) evaluate their performance with advanced and reliable computational methods, and (iii) summarize them in practical and reliable design rules and models to be used by engineers and practitioners. Although connections between steel and concrete are used ever since the commencement of reinforced concrete construction, there are several aspects which are yet to be fully understood. Advancement in technologies lead to development of new products such as post-installed anchors, anchor channels, high strength reinforcing bars etc., whose performance in concrete need to be investigated. New concrete based materials such as high performance concrete, fiber reinforced concrete, geopolymer concrete etc. are being developed and their compatibility with the steel components and rebar must be verified. The interaction between structure and the anchorages or concrete and steel structure connected through anchorages need to be understood. Innovative fastening solutions between steel and concrete components are being developed for which reliable design models are needed. Furthermore, several general design issues, e.g. anchorages with supplementary reinforcement, fatigue behavior of anchors, long term performance of bonded anchors, anchor channels under different loading combinations, harmonization of design between post-installed and cast-in place reinforcing bars, influence of corrosion on performance of anchorages and reinforcement etc. need in-depth investigations. In addition, globally, structures are exposed to natural and man-made hazards more than ever, which induce extreme loads on the structural components, e.g. earthquakes, fire, impact and combinations thereof. The performance of existing structures against such hazards has exposed several inherent weaknesses in the past. Often, the performance of structures under such hazards is significantly influenced by the performance of connections between steel and concrete. Since the loads induced in the structures by such hazards cannot be reliably estimated and also since under such loads, compatibility requirements between different components result in additional demands on different components, the designs can only be reliably done following a performance based design approach. Similar approaches must also be developed for the design of connections between steel and concrete to ensure a reliable performance from the connections and in turn from the structures against extreme hazards. One of the most important applications of anchorages is in strengthening of structures for connecting the strengthening element and the parent structure. Every strengthening needs a certain type of anchorage and the performance of the strengthening depends largely on the performance of the anchorage itself. The demands posed on the anchorages used in strengthening (e.g. seismic strengthening) could be very challenging, which includes high forces, large crack widths, combined load and crack cycling, limited area and depth to develop the required resistance etc. In order to ensure the safety of structures, therefore, it is essential to develop innovative strengthening methods along with anchorage techniques that would allow the strengthening to serve its desired function. The 3rd International Symposium on Connections between Steel and Concrete (ConSC2017) aims at bringing the experts from around the globe working in the field of steel-concrete connections to share and discuss the current state-of-the-art as well as the possible future directions to improve the safety of structures by making reliable connections between steel and concrete. The previous two symposia were held in Stuttgart in 2001 and 2007. This symposium offers a platform for the academicians, researchers, industry, regulatory authorities, practicing engineers and students to share the knowledge gained through a decade of research and development. With more than 120 high quality research papers along with the keynote addresses and invited lectures from the renowned experts, this symposium is a significant step forward towards the enhancement of knowledge as well as to provide food for thought for the forthcoming research in the field of connections between steel and concrete.
Open Access
Bidirectional loading history for seismic testing of 3D frame joints
(2021) Mahadik, Vinay; Sharma, Akanshu
Beam-column-joints (BCJ) in reinforced concrete (RC) frames are known to be critical against seismic actions. Hence, several researchers have conducted related investigations. The loading history used in the experimental investigations must be a sufficiently accurate and conservative representation of seismic loading on the structure and should trigger all possible critical failure mechanisms in the subassembly. Presently, there is significant diversity in the loading histories used for seismic investigation of structural subassemblies. This paper intends to propose an optimum loading history for considering bidirectional (horizontal) seismic action on 3D-RC BCJ subassemblies. To this end, the available loading histories (unidirectional and bidirectional) for simulation of seismic loads on RC joint subassemblies are reviewed in the context of the demands they impose on the joints. Finite element modeling and analyses are used as a tool for investigating the response of 3D-BCJ subassembly under different bidirectional loading states.
Open Access
Coupled thermo-mechanical inelastic analysis of reinforced concrete flexural members subjected to fire loads
(2016) Lakhani, Hitesh; Sharma, Akanshu; Hofmann, Jan
A simplified procedure to evaluate the complete-load-deflection time response of Reinforced Concrete (RC) flexural members subjected to fire loads is presented in this report. The proposed approach is extendable for performance evaluation of RC structures at all three levels of complexity namely member level (e.g. beams, columns), sub assembly level (e.g. beam-column joints) and as well as the structural level. This approach involves the determination of moment-curvature characteristics for the critical sections of the fire affected structural member and performing nonlinear static analysis to determine the load-deflection response of the member exposed to fire loads. The thermal analysis is first performed to determine the temperature distribution across the section, for a given fire duration. Temperature-dependent stress-strain curves for concrete and steel are then utilized to perform a moment-curvature analysis. The moment-curvature relationships are obtained at regular intervals of the fire exposure. These are then utilized to obtain the load-deflection plots following nonlinear static analysis (Pushover Analysis). The load-deflection plots obtained for the different exposure duration's are then used to obtain the deflection-time plots for a particular load level. Moreover, one of the important issues of modeling the initial stiffness giving due consideration to stiffness degradation due to material degradation and thermal cracking has been addressed in a rational manner. The approach is straightforward and can be easily programmed in spreadsheets. Implementation and validation of the proposed approach with various experiments available in literature has been discussed in detail in this report. The report also discusses the in-house code developed for carrying out 2D transient heat transfer analysis and obtaining moment-curvature relationships.
Open Access
Design recommendations for concrete pryout capacity of headed steel studs and post-installed anchors
(2023) Jebara, Khalil; Sharma, Akanshu; Ožbolt, Joško
Current formulas to assess the shear capacity of headed steel stud anchors and post-installed (PI) anchors in case of pryout failure (sometimes known as pull-rear failure) have been derived either based on the indirect-tension resistance model or are fully empirical based on push-out test results. In both cases, the predicted pryout capacity is clearly conservative and underestimates the true pryout capacity of anchorages, especially for stiff anchors with low embedment-to-diameter ratios (hef/d < 4.5). This paper proposes an empirical and a semi-empirical formula to predict the concrete pryout capacity of headed steel studs and PI anchors. They were derived based on an improved indirect-tension model which accounts for the stud diameter and the stud spacing in a group of anchors. Furthermore, a database of 214 monotonic shear tests from the literature, including own tests (push-off and horizontally shear tests), is reevaluated and compared to the provisions of EN1992-4. The scope of this assessment proposal includes single and group of headed steel studs and PI anchors attached to a stiff steel plate as well as shear connectors in composite structures without metal deck embedded in normal-weight concrete.
Open Access
Fire rating of post-installed anchors and rebars
(2020) Mahrenholtz, Philipp; Sharma, Akanshu
Fire safety is a critical performance aspect of construction products, and post-installed anchors and rebars are no exemption in that regard. During their service life, anchors and rebars are subjected to different kinds of load actions, so they have to be qualified and designed for critical safety performance. While the qualification guidelines for static and seismic loading have matured to conclusive requirements over the past two decades, the requirements for determining the resistance to fire are just about to consolidate. This contribution strives to provide clarity on the fire rating of post-installed anchors and rebars. For this, the current status of the regulations, as well as the underlying background, is reviewed after a brief introduction. Typical examples of fire ratings in the field of post-installed anchors and rebars are given, and recent research undertaken to close the last regulative gaps is briefly presented.
Open Access
Handbuch. I, Entwurf von Anschlüssen zwischen Stahl und Beton
(2014) Kuhlmann, Ulrike; Hofmann, Jan; Wald, Frantisek; Ruopp, Jakob; Sharma, Akanshu; Becková, Sárka; Schwarz, Ivo; Silva, Luis Simoes da; Gervásio, Helena; Gentili, Filippo; Krimpmann, Markus; Kann, Jörg van; Dehan, Véronique
Dieses Handbuch fasst die gewonnenen Forschungsergebnisse des Forschungsprojektes INFASO RFS-CR-2012-00022 "New Market Chances for Steel Structures by Innovative Fastening Solutions between Steel and Concrete" und des Nachfolgeprojekts RFS2-CT-2012-00022 "Valorisation of Knowledge for Innovative Fastening Solutions between Steel and Concrete" zusammen. Dieses Handbuch wurde von Wissenschaftlern zweier unterschiedlicher Forschungsbereiche verfasst. Aus dem Bereich der Befestigungstechnik vertreten durch das Institut für Werkstoffe im Bauwesen der Universität Stuttgart und aus dem Gebiet des Stahlbaus durch das Institut für Konstruktion und Entwurf der Universität Stuttgart und des Department of Steel and Timber Structures der Czech Technical University in Prague. Der Praxisbezug des Projektes wurde sichergestellt, indem Industriepartner und Organisationen maßgeblich am Entstehen beteiligt waren.
Open Access
Handbuch. II, Anwendung in der Praxis von Anschlüssen zwischen Stahl und Beton
(2014) Kuhlmann, Ulrike; Hofmann, Jan; Wald, Frantisek; Ruopp, Jakob; Sharma, Akanshu; Becková, Sárka; Schwarz, Ivo; Silva, Luis Simoes da; Gervásio, Helena; Gentili, Filippo; Krimpmann, Markus; Kann, Jörg van; Dehan, Véronique
Das zweite Handbuch basiert auf Handbuch I "Entwurf von Anschlüssen zwischen Stahl und Beton", in welchem die Forschungsergebnisse des RFCS Forschungsprojektes INFASO RFS-CR-2012-00022 "New Market Chances for Steel Structures by Innovative Fastening Solutions between Steel and Concrete" und des Nachfolgeprojekts RFS2-CT-2012-00022 "Valorisation of Knowledge for Innovative Fastening Solutions between Steel and Concrete" zusammengefasst sind. Innerhalb des Forschungsprojektes INFASO wurden Bemessungsprogramme für drei verschiedene Anschlüsse zwischen Stahl und Beton entwickelt. Diese Programme wurden im Forschungsprojekt INFASO+ überarbeitet. In diesem Handbuch werden Hintergrundinformationen zu den Bemessungsprogrammen gegeben und zusätzlich Anwendungsmöglichkeiten der Programme im Detail beschrieben.
Open Access
Load capacity of shallow embedded anchor channels
(2020) Mahrenholtz, Christoph; Sharma, Akanshu
Anchor channels are cast in concrete and allow the connection of components using channel bolts. In recent years, the design to value resulted in ever thinner concrete elements, which often cannot accommodate the required embedment depth of standard anchor channels. For this reason, channels may be fitted with short anchors. While existing design provisions allow for the calculation of the tension capacity also for shallow embedded anchor channels, tests are required to determine product-specific parameters for the economic shear loads design. The presented study investigated the performance of shallow embedded anchor channels tested in shear. The detailed evaluation of the test data demonstrates that testing of the minimum embedment is conservative and that the load-displacement behavior of channels with welded I-sections is comparable to that of channels with forged headed studs. In addition, a new evaluation approach is proposed.
Open Access
Numerical investigations on non-rectangular anchor groups under shear loads applied perpendicular or parallel to an edge
(2021) Bokor, Boglárka; Sharma, Akanshu
Anchorages of non-rectangular configuration, though not covered by current design codes, are often used in practice due to functional or architectural needs. Frequently, such anchor groups are placed close to a concrete edge and are subjected to shear loads. The design of such anchorages requires engineering judgement and no clear rules are given in the codes and standards. In this work, numerical investigations using a nonlinear 3D FE analysis code are carried out on anchor groups with triangular and hexagonal anchor patterns to understand their behavior under shear loads. A microplane model with relaxed kinematic constraint is utilized as the constitutive law for concrete. Two different orientations are considered for both triangular and hexagonal anchor groups while no hole clearance is considered in the analysis. Two loading scenarios are investigated: (i) shear loading applied perpendicular and towards the edge; and (ii) shear loading applied parallel to the edge. The results of the analyses are evaluated in terms of the load-displacement behavior and failure modes. A comparison is made between the results of the numerical simulations and the analytical calculations according to the current approaches. It is found that, similar to the rectangular anchorages, and also for such non-rectangular anchorages without hole clearance, it may be reasonable to calculate the concrete edge breakout capacity by assuming a failure crack from the back anchor row. Furthermore, the failure load of the investigated groups loaded in shear parallel to the edge may be considered as twice the failure load of the corresponding groups loaded in shear perpendicular to the edge.
Open Access
Review of testing and qualification of post-installed anchors under seismic actions for structural applications
(2021) Stehle, Erik Johannes; Sharma, Akanshu
During earthquakes, buildings are subjected to loads well beyond their usual demands, resulting in high stresses in the structural components and additional inertial forces coming from the non-structural elements. When post-installed anchors are used to form the connection between non-structural or structural members and the primary reinforced concrete structure, these anchors are also subjected to high seismic demands. To determine whether a post-installed anchor is suitable for such applications, it is assessed for its performance under seismic demands. In this review paper, the current European approach for testing and qualification of post-installed anchors under seismic actions is reviewed and discussed in the context of structural applications where anchors are used to form the connection between structural members that participate in the load-transfer mechanism against seismic loads. The first part of this paper provides a description of the testing procedures and the criteria against which the anchor performance is assessed. The procedures and assessment criteria are discussed regarding the suitability in the case of the above-described structural applications. In the second part, the qualification of anchors under seismic actions is discussed in the light of an upcoming performance-based design approach for anchors. In such an approach, information on the displacement and hysteretic behavior of an anchor in a broader range of the load–displacement curve is of vital importance. Therefore, additional testing approaches might be required in order to supplement the information on anchor performance provided in the current testing procedures. One such testing approach for pulsating tension load is reported.
Open Access
Seismic behavior and retrofitting of RC frame structures with emphasis on beam-column joints : experiments and numerical modeling
(2013) Sharma, Akanshu; Eligehausen, Rolf (Prof. Dr.-Ing.)
The vulnerability and poor seismic performance of the beam-column joints of old non-seismically designed reinforced concrete (RC) frame structures has been proven time and again, both at laboratory level as well as by natural disasters in real life situations. However, replacing a vast majority of existing structures designed with non-seismic considerations is not economically and practically viable. Such structures need to be correctly assessed to predict their seismic performance and retrofitted, if required. In order to realistically predict the seismic performance of such structures, practical and accurate models for simulating the inelastic joint behavior at structural level, are of utmost importance. Equally important is to associate realistic and practical hysteretic rules to capture the inelastic dynamic behavior of the structures. Assessment of existing structures using such tools can predict the seismic performance of the structures with high degree of confidence. Based on such assessment, a cost-effective and efficient retrofit solution can be designed and developed. Often, the retrofitting of such structures revolves around retrofitting of the beam-column joints. Thus, a need of practically viable retrofit solution for joints cannot be denied. This work is aimed at providing the practical solutions to the above-mentioned problems, through experimental and numerical modeling approach. Experiments have been performed first at the joint sub-assembly level to understand the behavior of poorly detailed joints with different anchorage details. To study the interaction of the various failure modes likely to occur in a non-seismically designed structure, experiment on a full-scale structure has been performed under pushover loads. Further, shake table tests were carried out on a 2D structure to verify the performance of joints at structural level under real life type seismic loads. These tests provided large database and helped in improving the overall understanding of the joint behavior under seismic loads. Fully fastened haunch retrofit solution (FFHRS) have been investigated as a viable retrofit option for poorly detailed joints. The solution has been tested through tests at sub-assembly level under cyclic loads as well as at structural level under dynamic loads. The results clearly displayed the efficacy of the FFHRS in safeguarding the joints thereby improving the global seismic behavior of structures. However, it is very important to confirm that the structural members shall not become shear critical due to the retrofit. It is also essential that the anchorage system used for fastening the haunch elements to frame members serve their purpose well. It was observed that the performance of the FFHRS in experiment on structure under dynamic loads is better than that in experiment on beam-column joints under cyclic loads. This is attributed partially to the phase difference between the force in anchor and crack opening and partially to instantaneous loading. To assess the seismic performance of structures giving due consideration to joint distortion, a new joint model has been presented. The model is based on realistic deformation of the joint sub-assembly and excellent agreement with the experimental results at sub-assembly as well as structural proves the efficacy and suitability of the model. To model the hysteretic behavior of the structure, an extension to pivot hysteretic model is presented. The model parameters are derived in a more rational way and can be applied at a wide range of structures. Further, a model is presented to simulate seismic behavior of joints retrofitted with FFHRS considering inelastic behavior of anchorage. The models were implemented in commercial software SAP2000. All the models have been vastly validated against experiments conducted by author as well as those available in the literature. In the end, the application of the models to assess and retrofit structures has been demonstrated by a real life case study.